The present invention relates generally to molded articles which may be blow molded such as a blow-molded ladder or a blow-molded staircase for a swimming pool.
Swimming pool ladders or staircases and various other articles have been made from a plastic material by a process known as “blow-molding,” as exemplified in commonly assigned U.S. Pat. No. 4,023,647 to Confer, commonly assigned U.S. Pat. No. 4,067,614 to Confer et al, and U.S. Pat. No. 4,166,833 to Schurman, all of which patents are hereby incorporated herein by reference. In the process of blow molding, a hollow thin-walled structure is formed having an exterior surface separated from an interior surface by the thin wall, and the hollow structure contains a fluid, in most cases air and/or water.
Walter, in U.S. Pat. No. 1,911,539, Doernemann, in U.S. Pat. No. 5,536,111, Troester, in U.S. Pat. No. 5,013,508, and Tokunaga, in U.S. Pat. No. 3,759,043, all disclose a three-dimensional polymeric structure having a male and a female interlocking component. Not one of these disclosures has both interlocking components on a single side of the structure. Moreover, these references disclose both interlocking components contacting the edges of the sides, which allow easier forces to separate the components. As such, none of these references discloses an apparatus that forms at least a male and a female interlocking component on a single side, and preferably not contacting an edge of the side, of the structure.
In commonly assigned U.S. Pat. No. 7,234,780; Lipniarski wrote, “A device and method for forming an indented female connector where the dimension of the indented female connector provides for removing a male molding component without damaging a set of internal ribs formed inside the female connector. A structure comprising an indented female blow-molded connector having a first wall having a top surface and a thickness, with the first wall surrounding an opening. At least one inner wall extends substantially perpendicular to the first wall and borders the opening. At least one rib is formed in the inner wall. A bottom wall is joined to the inner wall and the distance from the rib to the top surface is greater than the thickness of the first wall. The structure further comprising a male connector having a contact edge that, when positioned inside the indented female blow-molded connector, engage the at least one rib, such that the male connector and indented female blow-molded connector are releaseably joinable with one another. Structures can be made that use the indented female blow molded connectors and male connectors including braced stools having three or four legs.” This connection system requires the male component be inserted immediately into a female locking area (a.k.a., an immediate locking system), which is difficult for easy and secure assembly.
Since most blow molded polymeric materials have an immediate locking system, most blow molded polymeric materials having an immediate locking system also require additional interconnection devices be used to secure the assembly. Those additional interconnection devices include and are not limited to rods, screws and other conventional interconnection devices. See U.S. Pat. No. 6,769,513.
In commonly assigned U.S. Pat. No. 8,202,018, Lipniarski wrote, that “invention is directed to a blow molded plastic object having a female interconnection system comprising a receiving area and a locking area. We are aware of one patent that discloses a similar a female interconnection system. That patent is commonly assigned U.S. Pat. No. 6,190,600; which is hereby incorporated by reference. In that patent, Lipniarski wrote, ‘The present invention relates to an apparatus that forms a polymeric structure. The apparatus has a mold plate, a circular trench, a male and female interconnect, a vertical gap filler, and a cylinder. The mold plate has a predetermined geometric design. The circular trench is in the mold plate and the difference between the outer diameter and the inner diameter of the circular trench is a distance D. The male interconnect and the female interconnect are interspaced between each other. Each interconnect rotates within the circular trench and has a base and an interconnection portion. Each base has a width D and slidably mates to the mold plate. Each interconnect portion has a minimum width W which is less than D. The male interconnect portion protrudes downwards relatively from its base to a distance P, likewise the female interconnect portion protrudes upwards relatively from its base to a distance P. The vertical gap filler aligns with the circular trench and has a foundation and an extension. The extension has a width greater than W, a height greater than 2P, and protrudes upwards and downwards from its foundation. The cylinder rotates each interconnect to a predetermined position and raises the vertical gap filler so the foundation connects to the mold plate before any polymeric material is applied to the apparatus to form the polymeric structure. Once the polymeric structure is formed, the cylinder lowers the vertical gap filler until the extension is below the mold plate a distance greater than P and rotates each interconnect so the polymeric structure can be removed from the apparatus.”
The claimed device in U.S. Pat. No. 6,190,600 is a mold for creating a first blow molded object that had a first male structure having a first extension and a first block and a first female structure having first receiving area and a first inhibiting area; and a second blow molded object that had a second male structure having a second extension and a second block and a second female structure having second receiving area and a second inhibiting area. Thereby the first blow molded object and the second blow molded object could have the first male structure inserted into the second receiving area and the second male structure inserted into the first receiving area. Rotating the first blow molded object in relation to the second blow molded object so the first male structure slides into the second inhibiting area and the second male structure slides into the first inhibiting area. The first and second inhibiting areas have no blow molded locking mechanism to secure the respective male structures in the inhibiting areas. Instead the inhibiting areas rely on the walls (which surround [that means a back wall] the male structure except where the male interconnect slides from the receiving area to the inhibiting area and the male extension that protrudes through an opening in the female inhibiting area) to provide a friction fit to inhibit the male structure from releasing itself from the female structure. The lack of a locking mechanism is acceptable for wave dispersion systems but not for ladders which require a more secure system. The present invention solves this problem for blow molded structures that require a secure locking mechanism.